1. Field of the Invention
The present invention relates to an inkjet recording apparatus and a method of investigating ejection failure (non-ejection) determination performance, and more particularly, to an inkjet recording apparatus having a mechanism for checking the determination performance of an ejection failure determination test pattern.
2. Description of the Related Art
As an image forming apparatus, an inkjet recording apparatus (an inkjet printer) is known which comprises an inkjet head having an arrangement of a plurality of nozzles for ejecting ink as liquid droplets and which forms an image on a recording medium by ejecting the ink from the nozzles toward a recording medium, while causing the inkjet head and the recording medium to move relatively to each other.
Various methods are known as ink ejection methods for an inkjet recording apparatus of this kind. For example, known methods include: a piezoelectric method according to which a diaphragm that constitutes one portion of a pressure chamber (ink chamber) is caused to deform by the deformation of a piezoelectric element (piezoelectric ceramic), thereby changing the volume of the pressure chamber, ink being introduced from an ink supply channel into the pressure chamber when the volume of the pressure chamber is increased and ink being ejected from a nozzle in the form of a liquid droplet when the volume of the pressure chamber is decreased; and a thermal inkjet method according to which a gas bubble is created by heating ink, and the ink is ejected due to the expansive energy created as this gas bubble grows.
In an image forming apparatus having an inkjet head such as an inkjet recording apparatus, ink is supplied to the inkjet head via an ink supply channel from an ink tank which stores the ink, and the ink is ejected by the various ejection methods described above, but in order to form a high-quality image, it is necessary to perform the ejection in a stable fashion in such a manner that the ink ejection amount, ejection speed, ejection direction and shape (volume) of the ejected ink, and the like, are uniform at all times.
However, during printing, the nozzles of an inkjet head are filled with ink at all times in order that printing is carried out immediately when there is a print instruction, and the ink in the nozzles is exposed to air. Therefore, the ink in nozzles which do not perform ejection for a long period of time dries, the ink viscosity rises, suitable ink droplets cannot be ejected, and nozzle blockages or ejection failures occur. Furthermore, gas bubbles which have become intermixed into the ink supply channel, and the like, stagnate, shutting off the supply of ink, or if such ejection is continued for a long period of time, then ink refilling may be too slow and ejection defects may occur.
Due to these various causes, if an ejection failure occurs or it becomes impossible to achieve stable ink ejection, as described previously, then it becomes necessary to carry out maintenance of the ejection head. Therefore, various techniques are known for determining whether or not the ink has been ejected stably and whether an ejection failure has occurred in the inkjet head.
For example, a printing apparatus is known which records a prescribed test pattern at a prescribed resolution on printing paper by means of a recording head having a plurality of nozzles, and then judges nozzle abnormalities on the basis of data obtained by reading in and interpolating the test chart at a resolution lower than the resolution of the recording head, by means of a scanner (see, for example, Japanese Patent Application Publication No. 2007-54970, and the like).
Furthermore, there is also known a line inkjet printer which carries out printing with a fixed print head that is wider than the width of the print area on the printing paper, wherein a test pattern printed by staggering the ejection nozzle by a uniform interval in one portion of the paper is read in by a scanner unit which reads the print results in a wider area than the print width, the read test pattern is binarized, and an ejection failure check is carried out for all nozzles, every plurality of pages or every page (see, for example, Japanese Patent Application Publication No. 2004-9474, and the like).
Furthermore, technology is also known according to which printing is carried out onto recording paper using a print head in which a plurality of nozzles which eject ink are arranged so as to correspond to the full width of a print medium following a main scanning direction, integrated data is obtained by reading in the printed image with a line sensor and integrating the read pixel data thus obtained over a prescribed width in the recording paper conveyance direction, and unsuitable nozzles are identified by comparing the integrated data with the integral value of the expected reading data which is expected from the pixels where droplets ought to have been ejected (see, for example, Japanese Patent Application Publication No. 2005-67191).
Furthermore, technology is known according to which a printed test pattern is scanned and ejection failure nozzles are judged by determining nozzles where the quantity of light determined by a light sensor is equal to or lower than a threshold value (see, for example, Japanese Patent Application Publication No. 2006-335070).
Furthermore, for instance, technology is known according to which a chart for determining ejection failures in a recording head, constituted by a figure for determining individual nozzles, a figure for identifying a determination start position and a figure for identifying a determination reference position, is printed onto a conveyance belt which conveys a recording medium (see, for example, Japanese Patent Application Publication No. 2006-240232, or the like).
In an image output apparatus capable of recording an image over the whole width of the recording medium by scanning over a recording medium just once by inkjet recording, output from the respective nozzles of the inkjet head is performed sequentially, while leaving an interval therebetween, in such a manner that the presence or absence of output from each nozzle is investigated at a lower resolution than the output resolution. In this case, by adopting a determination pattern in which only the output from one nozzle in an output of high resolution is read with respect to one pixel on the output determination side which has low resolution, the presence or absence of output for each nozzle, in other words, whether or not the nozzle is in an ejection failure state, is judged by means of determination image data. Here, a captured image is subjected to binarization, image sharpening, or the like, under previously determined conditions, and even if the ink color or paper is changed, the output from the respective nozzles is determined under the same conditions.
If the number of determined ejection failure nozzles has exceeded a previously determined uniform value, then the operation of the image output apparatus is transferred to the maintenance mode. If the mode is transferred to the maintenance mode, then flushing, wiping, capping, or the like, is carried out, whereupon the mode is returned to the original normal image output mode.
However, in ejection failure investigation such as the related art examples described above, since the ejection failure determination itself is not normal, due to reasons such as inappropriate binarization processing or image sharpening, then image recording is carried out while the ejection failure continues and the image quality deteriorates, or conversely, the apparatus is transferred to maintenance mode when there is no actual need, and hence the image recording efficiency becomes worse.